Beware of Variations in Air Quality During the Spring and Fall

A simple yet crucial rule for ventilating poultry houses during cold weather is that air quality is directly proportional to the ventilation rate. More simply put, the fewer fans you operate, the worse your air quality will tend to be. This, of course, is not particularly shocking news to most, if not all, poultry producers. After all, ammonia concentrations tend to be highest during the winter months when ventilation rates tend to be at their lowest (Figure 1). But what is often underappreciate...d is how often this simple rule can be the root of bird health issues seen during the spring and fall.

During the winter months, especially with younger birds, a house will often operate in minimum ventilation mode both day and night. Since interval timer settings are typically not changed over the course of a day, the amount of fresh air entering a house will be the same at night as it is during the day and as a result, ammonia levels will remain relatively consistent, regardless of the time of day. Therefore, If ammonia levels are acceptable at 2 pm, for example they will likely be acceptable at 2 am (Figure 2).

During the spring and fall, the situation can be very
different (Figure 3). At night, fresh air is typically provided by minimum ventilation fans operating off an interval timer...for instance, two 36" fans operating 2 ½ minutes out of five. But during the day as outside temperatures start to rise, the house may start to warm a little causing the two 36" fans to operate constantly...a doubling of air exchange rates. By late afternoon, as outside temperatures continue to rise, a couple more 36" fans may turn on to keep house temperature in the proper range...a four-fold change in air exchange rates.

Let's say we are checking a house mid-afternoon when the four 36" fans are operating continuously and ammonia levels are found to be excellent...10 - 15 PPM. As the sun sets and outside temperatures begin to fall, two of the four, 36" fans will likely shut off, cutting the air exchange rate in half, and since ammonia levels are proportional to ventilation rate, they will most likely double to 20 - 30 PPM. Late in the evening, as temperatures continue to fall, the two 36" fans that will switch from cooling mode (operating continuously) to minimum ventilation mode (operating 2 ½ minutes out of five), thereby cutting the air exchange rate in half, resulting in a potential double of ammonia concentration to 40 - 60 PPM. The problem of course is a producer may not be checking on conditions late at night and as a result, high ammonia levels may potentially go unnoticed.

The larger the difference between daytime and nighttime ventilation rates, the greater the likelihood that conditions late at night could be adversely affecting bird performance and health. For instance, in Figure 3, on some days there was as much as a six-fold difference in ammonia concentrations from day to night, most likely resulting from a six-fold difference in ventilation rates from day to night.

It is important to note that though the wintertime flock’s daily average ammonia concentrations illustrated in Figure 1 were generally higher than those during the fall flock, the difference was relatively minimal, approximately 10 PPM. That being said, an argument could be made that the dramatically larger variations in ammonia concentrations observed during the fall flock may present a similar challenge to overall bird health as the slightly higher average daily ammonia concentrations seen during the winter flock.

Although high ammonia concentrations have been shown to affect bird weight gain and feed conversion in numerous studies, a less-often discussed adverse effect of high ammonia concentration is its impact on cilia in a bird's trachea. A bird's trachea is covered with a protective layer of sticky mucus. The purpose of mucus is to trap potentially pathogenic particulate matter (dust) from reaching the lower portions of a bird’s respiratory tract, where it is easier for pathogens to infect a bird. The cilia are very fine hair-like projections in the trachea whose job is to push the mucus up to a bird's trachea, where the pathogen-filled mucus can be swallowed and neutralized by the bird's acid-filled stomach. Although chronically high ammonia levels can damage cilia, short periods of high ammonia concentrations can temporarily paralyze them, preventing them from performing their essential job. As ventilation rates increase during the day and ammonia levels decrease, the cilia begin to function again; however, damage may have already been done, and the bird may already be infected with a wide range of potential harmful pathogens.

Of course, ideally, a producer would have an ammonia sensor connected to their environmental controller that would monitor ammonia levels when they are not present. However, ammonia sensors are still relatively expensive and typically only have a life of a couple of years. The good news is that a relatively inexpensive humidity sensor can serve a similar function. The fact is that, like ammonia concentration, a house's relative humidity will tend to vary from day to night as ventilation rates vary. If it is much more humid at night than during the day, chances are the ammonia levels are much higher at night than during the day. If humidity levels climb above 60%-70% late at night, it can be an indicator that ammonia levels were excessive (Figure 4).

One way for producers to avoid bird health issues during the spring and fall is to keep a close eye on ammonia concentrations first thing in the morning — the earlier, the better. Ideally, ammonia levels should be checked close to sunrise, when outside temperatures have not yet begun to rise and the house’s ventilation system is still operating in minimum ventilation mode. If ammonia levels and overall air quality are reasonable, it is likely that the situation was the same late at night as well.